Tritium is a beta emitter with a low energy emission spectrum. The maximum electron energy is 18.6 keV with a mean around 5.7 keV. Tritium has been employed in the past in gaseous form as the leading isotope for radioluminescent applications, such as emergency signs in aircraft and hospitals where maintenance-free/absolute reliability needs exist. These lighting devices operate by having tritium in gaseous form next to a phosphor material. The beta emission from the tritium causes optical excitation of the phosphor (such as zinc sulphide) which provides the light emission.
Limitations of these technologies include the fact that the only useful beta emitters are those that can be located near a phosphor. Most of the emitted electrons will fail to reach the luminescent materials, and without proper configuring, scale-up of the intensity/power level will be prohibitive. This is a direct result of the short emitted electron range in both gaseous and condensed phase media from a low energy beta emitter, such as a tritium. The range can vary from 6 mm in air to 6 microns in water to lengths that are substantially less than these distances in solid materials. But safety and environmental reasons dictate that only the lowest energy emitters (of which tritium is a prime candidate) be considered.
Another limitation is safety/environmentally related. Currently most utilization of tritium is in the gaseous form. In case of containment failure, the escape of tritiated gas into the environment is rapid and difficult to contain.